This invention relates generally to an improved torque responsive shut-off apparatus for pneumatically driven tools. More particularly, but not by way of limitation, the improved shut-off apparatus of this invention is responsive to inertial forces exerted on a weighted member to shut-off the air supply to the tool.
Shut-off devices previously constructed generally have been responsive to centrifugal forces or to spring forces which oppose such centrifugal forces to shut-off the air supply to the motor. For example, U.S. Pat. Nos. 3,904,305 issued Sept. 9, 1975 to Horace E. Boyd and 4,004,859 issued Jan. 25, 1977 to John A. Borries, each describe air tools that have speed responsive shut-offs. Each includes a valve that is opened by centrifugal weights and as the motor approaches the stall condition, that is, as the motor slows, a spring overrides the centrifugal force exerted by the weights to close the valve.
Most such devices shut-off before reaching the stall torque, but with speed controlled shut-off it is extremely difficult to accurately control the applied torque when the tool is used with both hard and soft joints.
An object of this invention is to provide an improved shut-off apparatus that stops the air supply to the motor prior to reaching stall torque.
Another object is to provide an improved shut-off device that consistently shuts-off at the desired torque.